Stripping voltammetric measurement of trace metal ions using screen-printed carbon and modified carbon paste electrodes on river water from the Eerste-Kuils River System

Abstract

Screen-printed carbon electrodes (SPCEs) and carbon paste electrodes (CPEs) were prepared as “mercury-free” electrochemical sensors for the determination of trace metal ions in aqueous solutions. SPCEs were coated with conducting polymer layers of either polyaniline (PANI), or polyaniline-poly(2,2′-dithiodianiline) (PANI-PDTDA). Furthermore, CPEs containing electroactive compounds with reactivity towards metal ions were employed to obtain enhanced selectivity. Optimised experimental conditions for Hg²⁺, Pb²⁺, Ni²⁺ and Cd²⁺ determination included the supporting electrolyte concentration, deposition potential (E _d) and accumulation time (t _acc). For the modified carbon paste sensors (MCPEs) it was found that −400 mV is an adequate deposition potential and an accumulation time of 120 s was adequate for the determination using the different constructed electrodes. Initial results showed linearity in the examined concentration range between 1 × 10⁻⁹ M and 1 × 10⁻⁶ M using the SPCE/PANI-PDTDA sensor on laboratory prepared standard solutions, while good selectivity for the different metal ions were obtained. Furthermore, the limit of detection (LOD) was determined for each of the sensors and for the SPCE/PANI-PDTDA sensor it was found to be 2.2 × 10⁻¹³ M, while for the SPCE/PANI sensor the LOD was determined to be 8.4 × 10⁻¹¹ M. The MCPE sensors also showed good linearity between the concentration range of 1 × 10⁻³ to 1 × 10⁻⁹ M. The LOD values for the various MCPE sensors, were found to be Hg(II) - 1.3 × 10⁻⁷ M; Cd(II) – 2.9 × 10⁻⁷ M; Ni(II) – 3.2 × 10⁻⁷ M; and Pb(II) – 1.7 × 10⁻⁷ M for the CPE/PANI-PDTDA sensor. For the CPE/PANI sensor the LOD values were Hg(II) – 1.5 × 10⁻⁵ M; Cd(II) – 8.6 × 10⁻⁷ M; Ni(II) – 9.5 × 10⁻⁷ M; and Pb(II) – 1.3 × 10⁻⁶ M. For the CPE/MBT sensor the LOD values were Hg(II) – 3.8 × 10⁻⁵ M; Cd(II) – 1.4 × 10⁻⁶ M; Ni(II) – 1 × 10⁻⁶ M; and Pb(II) – 6.3 × 10⁻⁵ M. Very low detection was obtained for the SPCE/PANI-PDTDA sensor in Hg²⁺ determination, while the MCPE sensors delivered sensitive simultaneous detection for Hg²⁺, Pb²⁺, Ni²⁺ and Cd²⁺ metal ions.

Keywords:

• Anodic stripping voltammetry
• modified carbon paste electrodes
• mercury
• lead
• nickel
• cadmium

Acknowledgments

This research was supported by funding received from the CSIR's parliamentary grant (PG) process, the Focus Area and RSA/Spain Bilateral Programmes of the National Research Foundation (NRF) of South Africa. The assistance of CSIR colleagues in the collection of samples is also acknowledged.